线段树——单点替换区间最值

#include <cstdio>
#include <algorithm>
using namespace std;

#define lson l , m , rt << 1
#define rson m + 1 , r , rt << 1 | 1
const int maxn = 222222;
struct Tree{
int value;
}tree[maxn<<2];

int max(int va,int vb){

return va>vb?va:vb;
}

void PushUP(int rt) {
tree[rt].value = max(tree[rt<<1].value , tree[rt<<1|1].value);
}
void build(int l,int r,int rt) {
if (l == r) {
scanf("%d",&tree[rt].value);
return ;
}
int m = (l + r) >> 1;
build(lson);
build(rson);
PushUP(rt);
}
void update(int p,int sc,int l,int r,int rt) {
if (l == r) {
tree[rt].value = sc;
return ;
}
int m = (l + r) >> 1;
if (p <= m) update(p , sc , lson);
else update(p , sc , rson);
PushUP(rt);
}
int query(int L,int R,int l,int r,int rt) {
if (L <= l && r <= R) {
return tree[rt].value;
}
int m = (l + r) >> 1;
int ret = 0;
if (L <= m) ret = max(ret , query(L , R , lson)); //得到左半段与之前比较的最大值
if (R > m) ret = max(ret , query(L , R , rson));  //得到右半段与之前比较的最大值
return ret;
}
int main() {
int n , m;
while (~scanf("%d%d",&n,&m)) {
build(1 , n , 1);
while (m --) {
char op[2];
int a , b;
scanf("%s%d%d",op,&a,&b);
if (op[0] == 'Q') printf("%d\n",query(a , b , 1 , n , 1));
else update(a , b , 1 , n , 1);
}
}
return 0;
}